Distribution of the Karamay dyke swarm is strictly controlled by the pre—existing extensional fractures，mainly with fl striking of 280。～ 300。． The minim um principal compressive stress was normal to these dykes．and the maxim um principal compressive stress was assumed to be vertica1． The dykes did not propagate as a single sheet but rather as fl set of discontinuous or continuous segments． The segmentation is partly attributable to the pre—existing fractures(30。～ 50。)that are oblique to the minimum compressive stress．The segments．which are oblique or parallel to the minimum compressive stress，tend to be thin or nearly absent． It is thus suggested that the intruding dykes activated these oblique fractures and were segm ented by the instantaneous decrease in the stress intensity factor at the tip of dyke segments as they reached these fractures．The major extension or elongation of the Karamay dyke swarm is 2．7 ．During Permian，northern Xinjiang was in fl postcollisional setting and was characterized by significant addition of mantle—derived magmas and their differentiates to the crust．The Karam ay dyke swarm was produced in an extensional regime and therefore may be one of the indicators of vertical growth of the continental crust．